1. Field of the Invention
This invention relates to the field of drilling techniques and drilling machinery for making holes in metal components, especially in sheet metal. More particularly, it pertains to drill templates or jigs for locating the proper position of holes to be drilled in a cambered workpiece and controlling a drilling machine or guiding an operator in making the holes.
2. Description of the Prior Art
In conventional practice, before a pattern of holes is drilled in a workpiece preparatory to installing rivets in the holes, a template or jig containing correctly located and directed holes conforming to the desired hole pattern is made and placed on the surface to be drilled. Then a drill, driven rotatably by a suitable motor, is inserted in each hole of the jig and forced against and through the workpiece sufficiently to accept the rivet to be placed in the holes. Often drill guide bushings, of hardened metal highly resistant to wear, are used with the jig to direct and guide the drill as it passes through the jig and into the workpiece.
Drill jigs and templates must have a thickness sufficient to establish accurately the location of the drill point on the workpiece and to direct correctly the drill as it passes through the jig and into the workpiece. When a drill guide bushing is used, the jig thickness must be large enough to grip and hold the bushing without movement throughout the drilling operation.
However, where the workpiece surface is cambered, as in the convexity of the curve of an airfoil from the leading edge to the trailing edge, especially in the vicinity of the leading edge where the airfoil contour changes form rapidly, the material and thickness of a conventional drill jig make the jig too stiff to conform to the surface to be drilled. It is preferred that a drilling template or jig be sufficiently flexible such that when placed on the curved surface of the workpiece it will bend readily, or under moderate pressure, into conformance with the contour to be drilled yet have sufficient thickness to hold a drill guide bushing or otherwise direct a drill and maintain its proper position. Furthermore, once formed to the shape of the workpiece, the drill template or jig should maintain its shape during the drilling operation while fixed rigidly in position on the workpiece.
Various techniques have been devised to drill accurately located and correctly directed holes in curved surfaces used in the fabrication of riveted airplane structures, such as wings and aerodynamic control surfaces.
U.S. Pat. No. 4,108,566 describes a drilling jig containing a hole pattern, the jig being of the conventional rigid type, preformed to the contour of the workpiece surface.
U.S. Pat. No. 3,158,045 describes a method and tools employed to locate apertures in structural components joined together by bolts, screws or rivets. The patent is concerned with replicating accurately in production tooling the dimensions and characteristics originally present in master tooling to which the production tooling is referenced.
A flexible drill jig that employs a soft rubber sheet supporting drill guide bushings is described in U.S. Pat. No. 2,417,539. Rubber or another elastomer is used in order that the sheet will conform to the cambered surface of an airplane wing. The drill guide bushings, held in place between lamina comprising the rubber sheet, are not rigidly supported. Instead, they are subject to longitudinal and rotational displacement from a true reference position and inclination due to the dimensionally unstable nature of the rubber sheet that supports and carries them.